Relationship between comb development, immune regulation, growth hormone, testosterone, and growth traits in Tianfu broilers

The comb, a secondary sexual characteristic in chickens, plays a crucial role in sexual selection, physiological regulation, and growth performance. This study explores the relationship between comb development, circulating hormone levels, and growth traits in Tianfu broilers. Weekly measurements of comb size and body weight from hatching to market age (day 70) revealed significant individual variations in comb traits. Based on comb size, chickens were categorized into large comb and small comb groups at market age. Histological analysis revealed that chickens with large combs exhibited thicker dermal, but the central layer exhibits the opposite, with sex-specific differences in collagen fiber content and epithelium thickness. Additionally, while only a few lymphocytes were observed in the combs of the large-comb group, focal lymphocyte aggregation was evident in the small-comb group. Circulating growth hormone (GH) and testosterone levels were significantly higher in chickens with large combs, particularly in roosters, where testosterone levels showed a significant correlation with testicular weight. It was observed that the GH levels were significantly correlated with comb development, independent of sex. Correlation analysis indicated a trade-off between comb size and carcass yield, suggesting that resource allocation favors ornamentation and reproductive system over meat production. These findings provide insights into the biological significance of comb development, emphasizing its potential as a marker for reproductive fitness and immunomodulatory functions in poultry breeding.